1. Field of the Invention
This invention relates to the fabrication of metal-ceramic articles of the type which are bonded together by an intermediate layer of mixed metal and ceramic.
2. Description of the Prior Art
The prior art has recognized that the stresses which arise from the difference in the coefficients of thermal expansion pose a major problem in the production of bonded metal-ceramic articles. This problem is discussed in the Ceramic Bulletin, Vol. 38, No. 6, 1959, pp. 301-307 and in the book Vacuum Sealing Techniques by A. Roth, published by Pergamon Press. One prior art solution involves the use of a graded layer between the metal and ceramic components with the intermediate layer being a mixture of metal and ceramic. The intermediate layer may be a graded layer in which the relative amounts of metal and ceramic vary from 100% metal at the metal interface to 100% ceramic at the ceramic interface. By the use of such a layer, the stresses caused by differential thermal expansion are distributed throughout a volume of material. The use of graded metal-ceramic seals made by powder techniques is described in Ceramic Age, February 1954, pp. 12-13. U.S. Pat. No. 3,091,548 describes a high temperature ceramic coating which is bonded to a metallic article with several intermediate layers of mixed ceramic-metal compositions.